"One Scroll Please" has a Play Effect. I suppose this could be something like "every time you play a card, get a tp scroll", but then why not use that wording? Seems to imply the mutations are actual cards played.

Theres a mutation Mode in Dota where for example with every hero kill you make your dmg done & taken is increased by 20%. Theres another mutation that you explode on death etc. Its a silly for fun game mode in dota and seems to be the same for artifact. It basically changes some of the core rules into silly ones.

I could definitely see mutation games bringing back people to Artifact. This seems similar to Hearthstone's "Tavern Brawls", which (from what I recall) were a pretty big hit, when the Tavern Brawl was well-made. Gives the more "casual" players a less grindy/tryhard mode to have fun in, which is great.

These mutations seem like extra cards (global play affects, like global improvements?) that you play down, as opposed to "the match starts with this in effect", but hopefully we see this released sooner rather than later!

Don't forget, back when Artifact was first showcased in an event, where you played the Call To Arms event decks against the casters (like Slacks and Luminous), the casters had 10 health disadvantage in every lane (same as the mutation "One Quarter Dead"), so it should be possible that they were in the game for a while.

After a second check, back in that event it did not influence Ancient Tower Health, so it could possibly be a different implementation.However, these are not actual cards for sure. I supposee they are used internally as "cards" added to the deck that you are supposed to play, the game does a check to see if you have a mutation card at the start of the game (Like Start Of The Game effects in Hearthstone) and burns that card off your deck, while activating its effect.